Diazomethane derivatives represented by the general formula (1) ##STR1## wherein Ar represents an aryl group which may be substituted are compounds useful as protective reagents for carboxyl groups contained in organic compounds.
Heretofore, the diazomethane derivatives represented by the general formula (1) are prepared from hydrazone derivatives represented by the general formula (2) ##STR2## wherein Ar is as defined above, for example, by processes (A) to (C) described below.
(A) A process which employs a metal oxide such as mercury oxide (Journal of Organic Chemistry, 24, 560, 1959), silver oxide (Journal of Organic Chemistry, 19, 718, 1954), nickel peroxide (Journal of Chemical Society, Chemical Communication, 20, 730, 1966), manganese dioxide (Japanese Examined Patent Publication No. 13222/1991), or the like.
(B) A process which employs an organic peroxide such as peracetic acid (Japanese Examined Patent Publication No. 34701/1984), m-chloroperbenzoic acid (Japanese Examined Patent Publication No.34701/1984, Indian Journal of Chemistry, 20B, 699, 1981), or the like.
(C) A process which employs an oxidizing agent other than those described above, such as hydrogen peroxide (Japanese Examined Patent Publication No. 34701/1984 and Japanese Examined Patent Publication No. 21942/1986), an N-substituted amine halide (Japanese Unexamined Patent Publication No. 170146/1984), or the like.
However, the above processes (A) to (C) have various drawbacks.
That is to say, process (A) has the problem of environmental pollution associated with the disposal of the metal oxide and the problem that even when the metal oxide is regenerated for re-use, a lot of attention must be paid for maintaining the activity thereof. Process (B) has the drawback that the organic peroxides themselves are expensive, in addition to the problem in safety and in the disposal such as removal of organic acids formed after the reaction. Process (C) has the problem in safety and the drawback that water is inevitably produced upon oxidation and lowers the concentration of hydrogen peroxide, resulting in a reduced reaction rate, and also entails the drawback that when said concentration is maintained in order to avoid said drawback by adding hydrogen peroxide, a considerably excess amount of hydrogen peroxide is required. Thus, in any of the above processes (A) to (C), consideration is necessary from a commercial viewpoints, and therefore these processes are not industrially advantageous.
On the other hand, a method is also known wherein the diazomethane derivatives obtained by the above-indicated methods is isolated and purified as crystals (Japanese Unexamined Patent Publication No. 11450/1985). However, the diazomethane derivatives are generally unstable to heat, and therefore they are used in the form of a solution as protective reagents. In this case, in addition to the yield, it is important to consider how to produce diazomethane derivatives of high purity, namely to consider how to suppress the formation of by-products such as azine compounds, which are usually formed during the production of the diazomethane derivatives.
Incidentally, Japanese Examined Patent Publication No. 34701/1984 and Journal of Chemical Society, Perkin I, 2030, 1975 disclose that when hydrazone derivatives are oxidized using an oxidizing agent such as an organic peracid, N-chlorosuccinimide, chloramine-T, hydrogen peroxide or the like, the oxidation is conducted in the presence of a phase transfer catalyst and an inorganic iodine compound under basic conditions. In these publications, there is a suggestion that sodium hypochlorite is an oxidizing agent.
However, in Japanese Examined Patent Publication No. 34701/1984, there is no working example in which sodium hypochlorite is used. In this publication, bases are merely used for the purpose of neutralizing acids such as acetic acid, which are formed when an organic acid such as peracetic acid is used.
On the other hand, Journal of Chemical Society, Perkin I, 2030, 1975 discloses a method which employs sodium hypochlorite and iodine I.sub.2. However, the yield is as low as 13% as shown in Table 4 on page 2032, and therefore it is set forth on page 2032, right column, lines 16-18 of this publication that in view of such a low yield, sodium hypochlorite is not suitable as an oxidizing agent.
Subsequently, concerning the use of hydrogen peroxide as an oxidizing agent, Japanese Examined Patent Publication No. 21942/1986 discloses a process in which the oxidation is conducted in the presence of an alkali metal carbonate and in the presence of a phase transfer catalyst and an inorganic iodine compound, while maintaining the concentration of hydrogen peroxide in the reaction system at 20% or higher. However, the yield of the product is 90% and still insufficient, and furthermore the diazomethane derivative of high purity is not obtained.